1. Field of the Disclosure
The present disclosure relates to a rotary connector that is assembled with a steering device of an automobile and is used as electrical connection means of an air bag system, and more particularly, to a rotary connector where a flat cable is reversely wound through an inverted portion of the flat cable in an receiving space defined between a stationary-side housing and a movable-side housing.
2. Description of the Related Art
A rotary connector is a connector in which a stationary-side housing including an outer cylindrical body and a movable-side housing including an inner cylindrical body are rotatably disposed coaxially with each other and flat cables are received and wound in a receiving space defined between the outer cylindrical body and the inner cylindrical body, and is used as electrical connection means of an air bag inflator that is mounted on a steering wheel, such as a steering device of an automobile, of which the number of times of rotation is finite. The flat cable is a strip-shaped body in which a conductor is supported on an insulating film, and a spiral type in which the flat cable is spirally wound and an inversion type in which the flat cable is wound so as to be inverted at a middle portion thereof have been known. Since the length of the flat cable can be significantly shortened in the latter, that is, the inversion type, it has become more mainstream.
In the related art, a rotary connector where a method of winding a flat cable includes an inversion type as described above, a roller holder in which a guide wall and a plurality of support shafts are erected on a ring-shaped rotating plate is turnably disposed in a receiving space, rollers are rotatably mounted on the respective support shafts of the roller holder, and an inverted portion of the flat cable passes through an opening formed between the guide wall and one roller facing the guide wall (as described in, for example, Japanese Unexamined Patent Application Publication No. 2006-86043). In the rotary connector having such a structure, when the movable-side housing rotates relative to the stationary-side housing in any one direction of a normal direction and a reverse direction, the flat cable is fed from the outer cylindrical body so as to be tightly wound on the inner cylindrical body or, conversely, is fed from the inner cylindrical body so as to be rewound on the outer cylindrical body according to the rotation direction of the movable-side housing. At that time, the inverted portion of the flat cable is moved in the same direction as the direction of the movable-side housing by a rotation angle smaller than the rotation angle of the movable-side housing, the roller holder is also moved in the same direction so as to follow the inverted portion, and the flat cable of which the length is about double the moving distances of the inverted portion and the roller holder is fed from the outer cylindrical body or the inner cylindrical body. That is, the roller holder receives a driving force (a pulling force or a pressing force) from the inverted portion of the flat cable and turns in the receiving space, and the movement of the flat cable in the radial direction is regulated by the plurality of rollers mounted on the roller holder as described above. Accordingly, the flat cable is smoothly fed from the outer cylindrical body and tightly wound on the inner cylindrical body, or is fed from the inner cylindrical body and rewound on the outer cylindrical body.
Further, a conventional rotary connector include a moving body supporting a planetary gear disposed in a receiving space instead of the roller holder and the moving body is rotated at the same speed as the speed of an inverted portion of a flat cable with the rotation (rotation and revolution) of the planetary gear (as described in, for example, Japanese Unexamined Patent Application Publication No. 8-280127). In such a rotary connector, a plurality of rollers are rotatably supported on the surface side of the moving body, and the inverted portion of the flat cable passes through an opening formed between arbitrary rollers. Furthermore, the planetary gear is rotatably supported on the back side of the moving body, and the planetary gear meshes with both an internal gear provided on a stationary-side housing and a sun gear provided on a movable-side housing. In the rotary connector having such a structure, when the movable-side housing rotates relative to the stationary-side housing, the planetary gear meshing with the internal gear and the sun gear rotates at a predetermined reduction gear ratio. Accordingly, the moving body supporting the planetary gear rotates and moves in the receiving space, and the inverted portion of the flat cable also moves in the receiving space at the same speed as the speed of the opening of the moving body.
Since the roller holder receives a driving force (a pulling force or a pressing force) from the inverted portion of the flat cable and turns in the receiving space in the rotary connector in the related art disclosed in Japanese Unexamined Patent Application Publication No. 2006-86043 as described above, suitable stiffness is necessary the flat cable passing through the opening (tensile strength corresponding to stiffness to be described below). For this reason, a flat cable of which the insulating film is thick and which has high stiffness should be used. In contrast, in the rotary connector in the related art disclosed in Japanese Unexamined Patent Application Publication No. 8-280127, it is possible to move the opening of the moving body and the inverted portion of the flat cable at the same speed in the same direction in the annular space by appropriately setting the gear ratio of the respective gears, including the planetary gear. Accordingly, since the moving body does not require a driving force applied from the inverted portion of the flat cable, a flat cable, which uses a thin insulating film, is inexpensive, and has low stiffness, can be used. However, the moving body supporting the planetary gear moves in the receiving space with the rotation of the planetary gear meshing with the internal gear and the sun gear. Accordingly, when a foreign matter, such as dust or sand, enters the receiving space through a clearance that is required at a sliding portion between the movable-side housing and the stationary-side housing, there is a concern that this foreign matter is deposited in the rotary connector and hinders the rotation of the planetary gear. In particular, when hard sand or the like of which the particle size is larger than the particle size of dust has entered the receiving space, such a foreign matter falls down in the receiving space and is likely to be deposited on the bottom plate of the stationary-side housing, for example, in a region below the internal gear. Accordingly, when the planetary gear passes below the internal gear, the planetary gear catches the foreign matter between the respective gears and cannot be rotated. For this reason, there is a problem in that the free rotation of the steering wheel is hindered.
These and other drawbacks exist.